The invention relates to a recirculating grinding mill, comprising: at least two rolling presses for comminuting the material to be ground, at least two first classifiers for classifying a coarse-grain fraction, at least one second classifier for classifying a fine-grain fraction and a medium-grain fraction from the fractions classified in the at least two first classifiers, the feedstock fed into the recirculating grinding mill passing the at least two rolling presses and the at least two first classifiers and then the at least one second classifier and the medium-grain fraction and the coarse fraction of the at least two first classifiers being fed once again to the rolling presses, and the at least two first classifiers being arranged underneath the at least two rolling presses.
In known recirculating grinding mills, feedstock to be ground is comminuted by a rolling press, in which the coarse material to be ground is passed through a narrow gap between two rolls. Depending on the nature of the material, press scabs thereby form and are broken up by further disagglomeration into the comminuted constituents. At the same time, the constituents that have not been comminuted to a small enough size are subjected to renewed comminution in the roll gap and the finer constituents are subjected to further classification, with the fine fraction being continuously removed from the recirculated material being ground. In order to maintain the recirculation of the material being ground, the press scabs and/or the material emerging from the disagglomeration stage are mechanically and/or pneumatically raised and fed again to the comminuting roll gap. A bucket mechanism is generally used for raising the material being ground, but combinations of pneumatic and mechanical lifting mechanisms have also proven effective in practice.
In order to increase the throughput of such mills, it is possible to operate more than one mill parallel next to one another, similar to a further mill. In order to save costs and plant expenditure, however, it is usual in this case to share the classifiers and/or the transporting arrangements between the recirculating grinding mills. The shared use of a mechanism, such as a classifier or elevator, also has the effect that a mixing of the fractions ground in the different mills takes place. As a result, this in turn avoids greatly varying grain size distributions in the fractions of different circuits.
However, there are usually limits to how much the plant capacity can be increased, as a result of limited availability of space and/or plant costs caused by the structural measures for maintaining and servicing the plant or for protecting it from the weather. In particular, the servicing expenditure of such a plant increases as the individual parts of the plant are installed closer together, since, for example, in this case the rolling presses or the movable parts of classifiers and/or lifting mechanisms can no longer be easily reached.